Type- and subtype-specific RT-PCR assays for avian influenza A viruses (AIV).

Reverse transcriptase (RT) PCR assays have been developed to improve the diagnosis of avian influenza A. RT-PCR using primers complementary to a conserved region of the matrix protein was assessed as being suitable for the detection of influenza A virus RNA from poultry as well as from pigs, horses and humans, regardless of the haemagglutinin (HA) and neuraminidase (NA) subtype. Therefore, this RT-PCR is a valuable tool to confirm the initial diagnosis of any influenza A infection. As a second approach, experiments were performed to identify the HA gene encoding the post-translational cleavage site of potentially highly pathogenic AIV isolates by RT-PCR. The principal aim was to design one universal primer pair for each virus subtype, H5 and H7, respectively, which allows the detection of all strain variants using only one consistent method. To realize this objective, it was necessary to develop 'wobble' primers. AIV RNAs from seven H5 and 11 H7 subtype viruses included in the investigations were specifically recognized by RT-PCR using these primers. This method therefore provides a rapid, subtype-specific diagnosis and subsequent sequencing of H5 and H7 avian influenza viruses.